The primary objective of this study will be to examine the hypothesis that lipid oxidation during low intensity exercise is reduced in obese versus lean individuals. This study will measure lipid and carbohydrate utilization during exercise and test the hypothesis that lipid oxidation during exercise is impaired in obesity. Lean and obese sedentary males will be recruited for this study. Defects in the regulation of skeletal muscle metabolism are present at rest in obese individuals, although information regarding substrate utilization during exercise in obesity is scarce. Body composition will be determined by DEXA. Substrate utilization during 60 minutes of exercise will be determined using indirect calorimetry and stable isotope tracers of free fatty acids (FFA) and glucose.